These early attempts at true multi-shot guns are cap & ball firearms that use a “slide” to move the next bullet into position (the slides resemble harmonicas, hence the name). There are three big disadvantages to this. The first is that the slide must be manually moved, turning even a pistol into a two-handed weapon. The second is that, given the manual action, it’s easily to misalign (and, after the first shot or two, the slide can become hot). The third is that the heft of the slide tends to unbalance the weapon.